SUMMARY: The studies of this project are those of the ongoing development and application of an in vivo, in situ animal model system using juvenile sheep for evaluating cardiac valves and cardiovascular flow dynamics. The studies use multiple disciplines of investigative techniques: surgery, -physiology, morphology and pathology, biomechanics, and the physical and chemical sciences. Previous years' studies have concentrated upon conventional hydraulic/hemodynamic evaluations of normal cardiac valves and prosthetic cardiac valvular substitutes, and upon morphologic and physical characterization the calcific degeneration of bioprosthetic valves. Efforts during the current year have emphasized studies of intracardiac flow dynamics for quantifying stenotic and regurgitant lesions. These studies demonstrate: 1) that observations of convergent flow using principles of momentum continuity preservation may be used to quantitate intracardiac flow volumes for both stenotic and regurgitant lesions; and 2) that clarification of both spatial (geometric) and temporal (pulsatility) characteristics are important in applying fundamental physical theories of fluid mechanics to the complexities of cardiac valvular flow dynamics.